pypy: don't try to fetch vendored dependencies for cffi bindings

Specifically, this affects _ssl and lzma.

This should be useful on Hydra/macOS where sandboxing is disabled.

pkgs/development/interpreters/python/pypy/default.nix

@@ -73,6 +73,8 @@ in with passthru; stdenv.mkDerivation rec {
   LD_LIBRARY_PATH = makeLibraryPath (filter (x : x.outPath != stdenv.cc.libc.outPath or "") buildInputs);
 
   patches = [
+    ./dont_fetch_vendored_deps.patch
+
     (substituteAll {
       src = ./tk_tcl_paths.patch;
       inherit tk tcl;

pkgs/development/interpreters/python/pypy/dont_fetch_vendored_deps.patch

@@ -0,0 +1,12 @@
+diff -ur a/lib_pypy/pypy_tools/build_cffi_imports.py b/lib_pypy/pypy_tools/build_cffi_imports.py
+--- a/lib_pypy/pypy_tools/build_cffi_imports.py	2021-04-12 01:11:48.000000000 -0400
++++ b/lib_pypy/pypy_tools/build_cffi_imports.py	2021-07-16 06:37:03.000000000 -0400
+@@ -225,6 +225,8 @@
+ 
+         print('*', ' '.join(args), file=sys.stderr)
+         if embed_dependencies and key in cffi_dependencies:
++            print("Nixpkgs: skipping fetching/building dependency", key)
++        elif False:
+             status, stdout, stderr = _build_dependency(key)
+             if status != 0:
+                 failures.append((key, module))